Production of lubricating oils by a combination catalyst system

ABSTRACT

A process for preparing a lubricating oil basestock having good low temperature properties. The process includes a first amorphous isomerization catalyst having a pore volume less than 0.99 ml/gm (H 2 O), an alumina content in the range of 30-50 wt % based on isomerization catalyst and an isoelectric point in the range of 4.5 to 6.5. The isomerization step is followed by a catalytic dewaxing step using an intermediate pore crystalline molecular sieve.

This application claims benefit of provisional application No.60/074,650 filed Feb. 13, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for preparing lubricating oilbasestocks. More particularly, a hydrocarbon feedstock is dewaxed bycontacting the feedstock with an amorphous isomerization catalystfollowed by a crystalline molecular sieve dewaxing catalyst.

2. Background of the Disclosure

In order to achieve the low temperature properties required for modernlubricating oil basestocks, it is usually necessary to dewax lubricatingbase oil feeds to remove waxy paraffins. It is well known that removalof waxy paraffins is needed to produce a base oil having the low pourpoints needed for acceptable cold flow properties.

Conventional methods for dewaxing include solvent dewaxing and catalyticdewaxing. It is difficult to economically produce a base oil which meetsthe low temperature properties required by present and future standardsfor engine oils. i.e., a high viscosity index (VI) and low pour point,from a conventional crude feedstock by solvent dewaxing alone,particularly as the VI and pour point demands are made increasinglystringent. Alternatives to solvent dewaxing include catalytic dewaxingby selective hydrocracking and/or catalytic dewaxing by waxisomerization. Both alternatives typically employ shape selectivecrystalline molecular sieves.

U.S. Pat. No.5,149,421 discloses a process for catalytically dewaxing ahydrocarbon feed by contacting the feed in the presence of hydrogen witha layered catalyst containing an intermediate pore sizesilicoaluminophosphate molecular sieve and a hydrogenation component,and an intermediate pore size aluminosilicate zeolite.

U.S. Pat. No.4,919,788 describes a process for producing a lubricatingoil basestock with a target pour point and high VI by dewaxing a feedwith a catalyst containing at least one large pore zeolite having ahydrogenation-dehydrogenation component to isomerize waxy paraffiniccomponents and selectively dewaxing the effluent by preferential removalof straight chain, waxy components. The selective dewaxing component canbe solvent or selective cat dewaxing. Selective cat dewaxing can beaccomplished by a zeolite such as ZSM-22 or ZSM-23.

EP 188,898 B1 relates to a process for dewaxing a feedstock bycontacting the feed with a crystalline zeolites having a ConstraintIndex less than 2 associated with a hydrogenation/dehydrogenationcomponent in a first stage followed by contacting the effluent from thefirst stage with a second stage catalyst containing a crystallinezeolite having a Constraint Index greater than 2 also associated with ahydrogenation/dehydrogenation component.

WO 96/07715 describes a process for producing a high VI lubricant from awaxy feed by a process in which the waxy feed is catalytically dewaxedprimarily by isomerization using a low acidity large pore zeoliteisomerization catalyst containing a noble metal hydrogenation componentfollowed by a second catalytic dewaxing step using a constrainedintermediate pore crystalline molecular sieve containing a metalhydrogenation/dehydrogenation component.

EP 744,452 relates to a process for producing lubricating base oils bycontacting hydrocracker bottoms with a catalyst comprising Pt and/or Pdon a refractory oxide carrier in the presence of hydrogen, separatingthe effluent from step 1 into a light and heavy distillate fraction andcatalytically dewaxing the heavy distillate fraction.

It would be desirable to have an economic process for selectivelyproducing a high VI, low pour point lubricating base oil under mildconditions to maximize yield and low temperature properties.

SUMMARY OF THE INVENTION

The present invention relates to a process for economically producing alubricating oil basestock with excellent low temperature properties bydewaxing a feedstock using a first amorphous isomerization catalystfollowed by a crystalline molecular sieve dewaxing catalyst. The processfor producing a lubricating base oil having good low temperatureproperties comprises:

(1) contacting a hydrocarbon feedstock with an amorphous silica-aluminabased isomerization catalyst having a pore volume less than 0.99 ml/gm(H₂O), an alumina content in the range of 35-55 wt % based onsilica-alumina and an isoelectric point in the range of 4.5 to 6.5, anda metal hydrogenation component in the presence of hydrogen to at leastpartially isomerize waxy paraffins in the hydrocarbon feedstock, and

(2) contacting at least a portion of the at least partially isomerizedfeedstock with a 10 or 12 ring shape selective intermediate porecrystalline molecular sieve containing a metal hydrogenation componentin the presence of hydrogen to at least partially catalytically dewaxthe feedstock from step (1).

The isomerization catalyst and the dewaxing catalyst can be contained ina single reactor in a layered configuration provided that the feed-stockfirst contacts the isomerization catalyst. Alternatively, theisomerization catalyst and dewaxing catalyst may be in separate reactorsprovided that the feedstock first contacts the isomerization catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial diagrammatic view showing a layered catalyst in asingle reactor in a process scheme for making lubricating oils.

FIG. 2 is a schematic flow diagram showing a two reactor system formaking lubricating oils.

FIG. 3 is a graph showing VI as a function of pour point for a CatalystA/Catalyst B stacked bed configuration vs. Catalyst B alone.

FIG. 4 is a graph showing yield as a function of pour point for aCatalyst A/Catalyst B stacked bed configuration vs. Catalyst B alone.

FIG. 5 is a graph showing VI as a function of pour point for a CatalystA/Catalyst C stacked bed configuration vs. Catalyst A/Catalyst Ccomposite vs. Catalyst C/alumina.

FIG. 6 is a graph showing 350° C.+ yield as a function of pour point fora Catalyst A/Catalyst C stacked bed configuration vs. CatalystA/Catalyst C composite vs. Catalyst C/alumina.

FIG. 7 is a graph showing VI as a function of pour point for a CatalystA first, Catalyst C second stacked bed configuration vs. a Catalyst Asecond, Catalyst C first stacked bed configuration.

FIG. 8 is a graph showing 350° C.+ yield as a function of pour point fora Catalyst A first, Catalyst C second stacked bed configuration vs. aCatalyst A second, Catalyst C first stacked bed configuration.

FIG. 9 is a graph of VI versus Pour Point (° C.) for three feeds forCatalyst C.

FIG. 10 is a graph of VI versus Pour Point (° C.) for three feeds forCatlayst E.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the invention, a hydrocarbon feedstock is dewaxed byfirst contacting the feedstock with an isomerization catalyst and theeffluent from this step contacted with a catalytic dewaxing catalyst toproduce a lubricating oil basestock having good low temperatureproperties. While the waxy paraffinic components of a typicalhydrocarbon feedstock possess good VI characteristics, it is necessaryto remove or isomerize most of the waxy paraffins in order to achieve abasestock having good low temperature properties, e.g., a low pour pointand a low Brookfield viscosity. Multi-ring aromatics and poly-cyclicnaphthenes possess poor VI and pour point properties, and it desirableto selectively remove these species from the lubricating basestockboiling range. The present process minimizes the amount of cracking tolight products not suitable as lubricating oil basestocks by selectivelyconverting a portion of the waxy paraffins to iso-paraffins andcompletes pour point reduction by catalytic dewaxing by selectivehydrocracking. By controlling the amount of cracking to light products,the yield of lube oil basestock is maximized.

The process according to the invention can process a wide variety ofwax-containing feedstocks including feeds derived from crude oils, shaleoils and tar sands as well as synthetic feeds such as those derived fromthe Fischer-Tropsch process. Typical wax-containing feedstocks for thepreparation of lubricating base oils have initial boiling points ofabout 315° C. or higher, and include feeds such as reduced crudes,hydrocrackates, raffinates, hydrotreated oils, atmospheric gas oils,vacuum gas oils, coker gas oils, atmospheric and vacuum resids,deasphalted oils, slack waxes and Fischer-Tropsch wax. Such feeds may bederived from distillation towers (atmospheric and vacuum),hydrocrackers, hydrotreaters and solvent extraction units, and may havewax contents of up to 50% or more. Optionally, such feeds may be solventdewaxed prior to the process of the invention.

Hydrocracking, hydrotreating and solvent extraction are well known inthe art. Typical hydrocracking catalysts have a large pore size, andcontain an acidic functionality as well as a hydrogenation component.Examples include amorphous materials such as alumina and silica-aluminaand crystalline alumino-silicate materials such as zeolite X zeolite Y,and ZSM-20. Hydrocracking accomplishes ring opening as well assaturation of aromatic compounds to yield hydrocracked products of amore paraffinic character. Typical hydrocracking conditions includehydrogen pressures of from 10,335 to 17,238 kPa (1,500 to 2,500 psia),temperature of from 343 to 427° C., liquid hourly space velocity of 0.5to 2 and hydrogen treat gas rate of 356 to 1780 m³/m³ (2,000 to 10,000Scf/bbl).

Hydrotreating of feeds is directed to heteroatom removal as well assaturation of aromatics. Since nitrogen and sulfur containing compoundsmay be detrimental to dewaxing catalysts, feeds are hydrotreated tolower nitrogen- and sulfur-containing species to less than about 20ppmw, preferably less than 10 ppmw. The nitrogen- and sulfur-containingspecies are converted under hydro-treating conditions to hydrogensulfide and ammonia, which are typically removed by, e.g., strippingprior to the dewaxing steps. Typical hydrotreating catalysts arenon-noble metal Group VIII and/or Group VIB metals on a weakly acidicinorganic support such as alumina. Examples of hydrotreating catalystsinclude Co/Mo, Ni/Mo or Co/Ni/Mo all on alumina. Hydrotreating reactionconditions are described in EP 225,053 B1.

Waxy feeds secured from natural petroleum sources contain quantities ofsulfur and nitrogen compounds which are known to deactivate waxhydroisomerization catalysts. To prevent this deactivation it ispreferred that the feed contain no more than 10 ppm sulfur, preferablyless than 2 ppm sulfur and no more than 2 ppm nitrogen, preferably lessthan 1 ppm nitrogen.

To achieve these limits the feed is preferably hydrotreated to reducethe sulfur and nitrogen content.

Hydrotreating can be conducted using any typical hydrotreating catalystsuch as Ni/Mo on alumina, Co/Mo on alumina, Co/Ni/Mo on alumina, e.g.,KF-840, KF-843, HDN-30, HDN-60, Criteria C-411, etc. Similarly, bulkcatalysts comprising Ni/Mn/Mo or Cr/Ni/Mo sulfides as described in U.S.Pat. No. 5,122,258 can be used.

Hydrotreating is performed at temperatures in the range 280° C. to 400°C., preferably 340° C. to 380° C. at pressures in the range 500 to 3000psi, hydrogen treat gas rate in the range of 500 to 5000 SCF/bbl and aflow velocity in the range 0.1 to 5 LHSV, preferably 1 to 2 LHSV.

Solvent extraction is used to separate aromatics includingheteroatom-containing species from paraffinic hydrocarbons. Typicalsolvents include phenol, N-methyl-2-pyrrolidone and furfural. Theraffinate from solvent extraction which may be hydrotreated if desiredto lower nitrogen and sulfur content can be used as a feedstock in thepresent invention.

If it is desired to remove wax as a valuable product the feedstock canbe solvent dewaxed prior to catalytic dewaxing by using typical solventdewaxers such as propane, butane, methyl ethyl ketone, methyl isobutylketone and mixtures thereof. The ketones can be combined with othersolvents such as benzene, toluene and xylene.

Solvent dewaxing typically involves mixing the feed with chilleddewaxing solvent to form an oil-solvent solution and precipitated wax isthere after separated by, for example filtration. The temperature andsolvent are selected so that the oil is dissolved by the chilled solventwhile the wax is precipitated.

A particularly suitable solvent dewaxing process involves the use of acooling tower where solvent is pre-chilled and added incrementally atseveral points along the height of the cooling tower. The oil-solventmixture is agitated during the chilling step to permit substantiallyinstantaneous mixing of the pre-chilled solvent with the oil. Thepre-chilled solvent is added incrementally along the length of thecooling tower so as to maintain an average chilling rate at or below 10°F./minute, usually between about 1 to about 5° F./minute. The finaltemperature of the oil-solvent/precipitated wax mixture in the coolingtower will usually be between 0 and 50° F. (−17.8° C. to 10° C.). Themixture may then be sent to a scraped surface chiller to separateprecipitated wax from the mixture.

In general, the amount of solvent added will be sufficient to provide aliquid/solid weight ratio between the range of 5/1 and 20/1 at thedewaxing temperature and a solvent/oil volume ratio between 1.5/1 to5/1. The solvent dewaxed oil is typically dewaxed to a pour point lessthan about +10° C.

In the process according to the invention, the hydrocarbon feedstock ispassed sequentially through a catalyst system containing a firstamorphous hydroisomerization catalyst followed by a shape selectivecatalytic dewaxing catalyst. While both isomerization and catalyticdewaxing can be used to dewax a waxy feed, they accomplish dewaxing bydiffering reaction routes. In the case of bifunctional catalysts(molecular sieve plus active metal component), the nature of thedewaxing results for waxy paraffins is dependent on several factorsincluding the reaction temperature and pressure, the nature of the metaland the nature and number of available acidic sites, especially thedensity and strengths of acidic sites. While not wishing to be bound toany particular theory or reaction mechanism, it appears that the initialstep with either mode of dewaxing is the formation of olefins at theactive metal sites followed by the formation of carbenium ions at theacidic sites. If the primary means of reaction of these intermediateions is isomerization, then the hydroisomerized products will bebranched paraffins, i.e., iso-paraffins and molecules still useful ascomponents of lubricating base oils. On the other hand, if the primarymeans of reaction of the intermediate ions is selective hydrocracking,then a portion of the reacted paraffins will be removed from thelubricating basestock boiling point range. Most catalytic dewaxingcatalysts perform in a combination of these two modes to some degree.Selective hydrocracking also known as catalytic dewaxing isdistinguished from hydrocracking in that the former shows significantpreference for reaction of paraffinic molecules. In general, catalyticdewaxing by selective hydrocracking or paraffin hydroisomerization takesplace under milder reaction conditions than those conditions forhydrocracking.

The isomerization catalyst in the present process is an amorphous(non-crystalline) material. In the case of crystalline materials such asalumino-silicates, aluminophosphates and silicoalumino phosphates,selectivity for isomerization is achieved in part by controlling thenature of pore openings. Large pore zeolites having pore diametersgreater than 7.0 Å and high silica to alumina ratios (low acidities) areemployed for isomerization.

In the case of amorphous isomerization catalysts according to theinvention, isomerization selectivity is controlled by a combination ofacidity, pore volume, alumina content and isoelectric point.

A useful scale of acidity for catalysts is based on the isomerization of2-methyl-2-pentene as described by Kramer and McVicker, J. Catalysis,92, 355 (1985). In this scale of acidity, 2-methyl-2-pentene issubjected to the catalyst to be evaluated at a fixed temperature,typically 200° C. In the presence of catalyst sites, 2-methyl-2-penteneforms a carbenium ion. The isomerization pathway of the carbenium ion isindicative of the acidity of active sites in the catalyst. Thus weaklyacidic sites form 4-methyl-2-pentene whereas strongly acidic sitesresult in a skeletal rearrangement to 3-methyl-2-pentene with verystrongly acid sites forming 2,3-dimethyl-2-butene. The mole ratio of3-methyl-2-pentene to 4-methyl-2-pentene can be correlated to a scale ofacidity. This acidity scale ranges from 0.0 to 4.0. Very weakly acidicsites will have values near 0.0 whereas very strongly acidic sites willhave values approaching 4.0. The isomerization catalysts useful in thepresent process have acidity values of from about 0.5 to 2.5, preferably0.5 to 2.0. The acidity of metal oxide supports can be controlled byadding promoters and/or dopants, or by controlling the nature of themetal oxide support, e.g., by controlling the amount of silicaincorporated into a silica-alumina support. Examples of promoters and/ordopants include halogen, especially fluorine, phosphorus, boron, yttria,rare-earth oxides and magnesia. Promoters such as halogens generallyincrease the acidity of metal oxide supports while mildly basic dopantssuch as yttria or magnesia tend to decrease the acidity of suchsupports.

The amorphous isomerization catalyst is a silica-alumina based catalysthaving a pore volume less than 0.99 ml/gm (H₂O), preferably less than0.8 ml/gm (H₂O), and most preferably less than 0.6 ml/gm (H₂O). As isknown in the art, the term “pore volume (H₂O) refers to pore volumemeasured by drying the catalyst to about 500° C., weighing the driedcatalyst, immersing it in water for 15 minutes, removing the materialfrom the water and centrifuging to remove surface water. Then thematerial is weighed and the pore volume is determined from thedifferences in weight between the dried catalyst and the lattermaterial.

In addition to its pore volume, the silica-alumina of the catalyst isfurther characterized as having an alumina content in the range of 35 to55 wt %, preferably 35 to 50 wt %, most preferably 38 to 45 wt %, basedon the isomerization catalyst.

Another criteria of the silica-alumina used in the isomerizationcatalyst is that it has an isoelectric point from 4.5 to 6.5. As isknown in the art, the isoelectric point of a material depends on therelative concentration and the acidity (pK_(a)/pK_(b)) of surfacespecies (G. A. Parks, Chem. Review, 177-198 (1965)).

Optionally the silica-alumina based catalyst material can be promoted ordoped with e.g., yttria or with a rare earth oxide, e.g., La, Ce, etc.,or with e.g., boria, magnesia. In this particular embodiment, theisoelectric point will increase depending on the dopant and dopant levelto a level not more than 2 points higher than that of the basesilica-alumina.

The isomerization catalyst also contains a metal hydrogenation componentwhich may be at least one of a Group VIB and Group VIII metal,preferably a Group VIII metal, more preferably a Group VIII noble metal,especially Pt, Pd, or mixtures thereof The amount of metal hydrogenationcomponent is from 0.1 to 30 wt %, based on isomerization catalyst,preferably from 0.3 to 20 wt %.

The hydroisomerization process utilizing the catalyst of the presentinvention is conducted at temperatures between about 200° C. to 400° C.,preferably 250° C. to 380° C., and most preferably 300° C. to 350° C. athydrogen partial pressure between about 350 to 5000 psig (2.41 to 34.6mPa), preferably 1000 to 2500 psig (7.0 to 17.2 mPa), a hydrogen gastreat ratio of 500 to 10,000 SCF H₂/bbl (89 to 1780 m³/m³), preferably2,000 to 5,000 SCF H₂/bbl (356 to 890 m³/m³) and a LHSV of 0.1 to 10v/v/hr, 0.5 to 5 v/v/hr, preferably 1 to 2 v/v/hr.

By choosing relatively mild conditions, isomerization of waxy components(n-paraffins and slightly branched paraffins) to isoparaffinic materialscan be accomplished with a minimum of cracking to non-lube (boilingbelow 343° C.) products. While these isoparaffinic materials may have ahigh VI, some individual species may also may have pour points too highto meet the low temperature requirements of modem basestocks. Also, itis not feasible to isomerize all of the waxy components in the feed.Thus there is a need to catalytically dewax the products from this firststage to lower the pour point to desired target range.

Catalysts useful in the catalytic dewaxing step include crystalline 10and 12 ring molecular sieves and a metal hydrogenation component.Crystalline molecular sieves include metallo-, e.g., alumino silicates,alumino phosphates and silicoaluminophosphates. Examples of crystallinealumino silicates include zeolites such as ZSM-5, ZSM-11, ZSM-12,Theta-1 (ZSM-22), ZSM-23, ZSM-35, ZSM-48 natural and syntheticferrierites, ZSM-57, Beta Mordenite and Offretite. Examples ofcrystalline alumino and silicoalumino-phosphates include SAPO-11,SAPO-41, SAPO-3 1, MAPO-11 and MAPO-31. Preferred include ZSM-5, ZSM-22,ZSM-23, ferrierites, and SAPO-11.

The dewaxing catalyst may also contain an amorphous component. Theacidity of the amorphous component is preferably from 0.5 to 2.5 on theKramer/McVicker acidity scale described above. Examples of amorphousmaterials include silica-alumina, halogenated alumina, acidic clays,silica-magnesia, yttria silica-alumina and the like. Especiallypreferred is silica-alumina.

The dewaxing catalyst may also include a matrix or binder which is amaterial resistant to process conditions and which is substantiallynon-catalytic under reaction conditions. Matrix materials may besynthetic or naturally occurring materials such as clays, silica andmetal oxides. Matrix materials which are metal oxides include singleoxides such as alumina, binary compositions such as silica-magnesia andternary compositions such as silica-alumina-zirconia.

If the dewaxing catalyst contains an active amorphous component, thecrystalline molecular sieve/metal hydrogenation component/amorphouscomponent may be composited together. In the alternative disclosedherein, the crystalline molecular sieve and amorphous component can bein a layered configuration wherein it is preferred the top layer in thereaction vessel is the amorphous component and the lower layer is thecrystalline molecular sieve. In this alternative configuration it ispreferred that the metal hydrogenation component be present on bothcomponents.

The metal hydrogenation component of the dewaxing catalyst may be atleast one metal from the Group VIB and Group VIII of the Periodic Table(published by Sargent-Welch Scientific Company). Preferred metals areGroup VIII noble metals, especially palladium and platinum. Metals maybe added to the catalyst by means well known in the art such as metalimpregnation with a soluble salt.

The dewaxing catalyst may contain, based on the weight of totalcatalyst, from 5 to 95 wt % of crystalline molecular sieve, from 0 to 90wt % of amorphous component and from 0.1 to 30 wt % of metalhydrogenation component with the balance being matrix material.

Process conditions in the catalytic dewaxing zone include a temperatureof from 260 to 420° C., preferably 270 to 400° C., a hydrogen partialpressure of from 2.41 to 34.5 mPa (350 to 5000 psi), preferably 5.52 to20.7 mPa, a liquid hourly space velocity of from 0.1 to 10 v/v/hr,preferably 0.5 to 3.0, and a hydrogen circulation rate of from 89 to1780 m³/m³ (500 to 10000 scf/bbl), preferably 178 to 890 m³/m³.

The amount of dewaxing by selective hydrocracking to lower boilingmaterials will be a function of the nature of the isomerate from theisomerization zone, the dewaxing properties of the molecular sievechosen and the desired target pour point. In general, the lower the pourpoint chosen, the greater the conversion to lower boiling point non-lubeproducts because more severe selective hydrocracking conditions will berequired.

The process of the invention may occur by using a single reactorcontaining two separated beds of isomerization and dewaxing catalyst, ormake take place in separate reactors, e.g., a cascade reactor system inwhich the first reactor contains the isomerization catalyst and thesecond reactor the dewaxing catalyst optionally with inter-reactorseparation of the liquid and gaseous products with the liquid productsbeing further processed in the dewaxing reactor. Either configurationsoffers advantages over a single catalyst system, including those inwhich the two respective dewaxing functions are combined into a singleor composite catalyst.

Each catalyst phase may be used at its ideal reactor conditions toobtained the desired final basestock properties. If the targetproperties are high VI and lower viscosities, then the reactorconditions can be made more severe in first bed of isomerizationcatalyst. This will result in lower lube basestock yields. On the otherhand, if a higher yield is the desired result, then the severity of theconditions in the first isomerization catalyst bed should be reduced.This will result in lower VI and higher viscosities.

As normal catalyst deactivation occurs, it is expected that the twocatalyst will deactivate at different rates. The separate temperaturecontrol possible for the individual catalyst beds will allow maintenanceof the desired conversion rates over each respective catalyst. Also,separate temperature control allows the operator to rapidly andefficiently adjust operation of the separate beds to meet productquality/quantity objectives. The layered or stacked bed configurationpermits much greater feed flexibility over traditional dewaxing. Forexample, feeds may have widely varying wax contents. Finally, the firstisomerization bed increases the relative pour point reduction activityof the second dewaxing bed. This may occur due to the cracking out andsaturation of some fraction of the aromatics present in the feedstock aswell as by the isomerization of a fraction of the wax present in thefeedstock, particularly those higher carbon number wax molecules whichmay be more difficult for a molecular sieve catalyst to isomerize orcrack from the feedstock.

The process is further exemplified in FIGS. 1 and 2. FIG. 1 is aschematic flow diagram showing a layered catalyst configuration. In FIG.1, hydrogen gas enters reactor 10 through line 12. Heated feedstock isadded to reactor 10 through line 14 where it is distributed over thereactor diameter by plate 16. After passing through distributor 16, feedcontacts catalyst bed 18 containing amorphous isomerization catalyst.Catalyst bed 18 is heated to the desired temperature by hot gas such assteam or other heating means entering line 20 to heating coil 22 andexiting through line 24. Feedstock, which is at least partiallyisomerized in catalyst bed 18, flows through separator 26. Separator 26has sides with openings of such size as to admit hydrogen and feed butnot catalyst. Isomerized feed is then conducted to a second distributionplate 28 through conduit 30. Upon passing through distributor 28,isomerized feed contacts catalytic dewaxing bed 32. Catalyst bed 32 isalso heated to the desired temperature by circulating hot gas enteringthrough line 34 to heating coil 36 and exit line 38. The temperature inbed 32 may be different from bed 18 to achieve the desired conversionlevel and product quality. Dewaxed product then exits bed 32 by passingthrough separator 40 where it is collected in collector 42. Hydrogen gasexits reactor 10 by line 44.

FIG. 2 is a schematic flow diagram showing another embodiment of theinvention. Heated feedstock enters reactor 11 through line 15. Hydrogengas is admitted to reactor 11 via line 17. Feedstock passes throughdistributor 19 to catalyst bed 21 containing amorphous isomerizationcatalyst. Reactor 11 is heated to maintain the desired temperature incatalyst bed 21 by heating coils (not shown). The at least partiallyisomerized feedstock is separated from catalyst via separator and isconducted through line 25 to heat exchanger 27. After being heated tothe desired temperature, isomerized feedstock is passed to pump 29 andon to reactor 31 via line 35. Hydrogen gas from reactor 11 is conductedto reactor 31 by line 33. Make-up hydrogen can be added to line 33 ifdesired. Upon entering reactor 31, isomerized feedstock passes throughdistributor 37 where it is then contacted with catalyst bed 39containing dewaxing catalyst. Reactor 31 is heated to maintain thedesired temperature in catalyst bed 39 by heating coils (not shown). Thetemperature in reactor 31 may be different from that of reactor 21 andis adjusted as needed to maintain the desired conversion level andproduct quality. Dewaxed feedstock is then separated from catalyst byseparator 41 and is withdrawn via line. Hydrogen gas is withdrawn fromreactor 31 by line 45.

The total liquid product from either the layered catalyst system of FIG.1 or the two reactor system of FIG. 2 may require post-treatment toadjust product quality parameters such as color, toxicity, or haze.Hydrofinishing is commonly employed to adjust such product qualityparameters. Process conditions for hydrofinishing are mild to minimizeproduct loss through cracking. Conventional hydrofinishing catalystsinclude non-noble metal Group VIII and/or Group VI metals such as Ni/Mo,Co/Mo, Ni/W, Ni/Co/Mo and the like on non-acidic or weakly acidicsupports such as silica or alumina. The catalyst may be activated priorto use by sulfiding or other conventional method.

Reaction conditions in the hydrofinishing unit are mild and include atemperature of from 260° C. to 360° C., preferably 290° C. to 350° C.,more preferably 290° C. to 330° C., a hydrogen partial pressure of from1000 to 2500 psig (7.0 to 17.3 mPa), preferably 1000 to 2000 psig (7.0to 13.9 mPa), a space velocity of from 0.2 to 5.0 LHSV, preferably 0.7to 3.0 LHSV, and a hydrogen to feed ratio of from 500 to 5000 SCF/bbl(89 to 890 m³/m³), preferably 2000 to 4000 Scf/bbl (356 to 712 m³/m³).The catalyst in the cold hydrofinishing unit may be the same as in thefirst hydroconversion unit. However, more acidic catalyst supports suchas silica-alumina, zirconia and the like may be used in the coldhydrofinishing unit.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLES Example 1

In this example, a waxy hydrocracker bottoms feedstock designated asHCIS, was hydroconverted over a 0.5% Pt/4.0% yttria on silica-aluminacatalyst with a pore volume of 0.54 ml/gm (H₂O), and alumina content of45 wt % based on silica-alumina and an isoelectric point of 6.08(designated as Catalyst D), over a Pd/Pt on ferrierite based catalyst(designated as Catalyst B), and over both catalysts in a cascadedreactor sequence. In all cases the reactor pressure was 1000 psig ofhydrogen at a flow rate of 2500 scf/bbl.

Catalyst D Alone

The following data was obtained for hydroconversion using only 0.5% Pton silica-alumina (Catalyst A), which does not reduce pour points to thedesired levels, follow by solvent dewaxing (SDW).

TABLE 1 Catalyst D Pour Grams Dry Wax Dewaxed Point Wax in ConvertedCalculated Oil 350° C.+ Reactor after 350° C.+ to Oil or Dewaxed YieldYield Temp. SDW per 100 350° C.− Oil Yield Loss (%) VI (° C.) (° C.)grams feed Products (%) (%) SDW - Waxy Product 86 112 Solvent −22 18.0 —67.9 — Dewaxed Hydro-Converted Products 75 117 340 −23 12.8 29% 62.2 5.770 117 340 −23 12.6 30% 57.4 10.5 73 120 340 −19 11.7 35% 61.3 6.6 61118 360 −24 8.5 53% 52.5 15.4 61 120 360 −17 10.4 42% 50.6 17.3 63 118360 −19 11.3 37% 51.7 16.2 75 117 340 −20 13.5 25% 61.5 6.4 74 117 340−21 13.3 26% 60.7 7.2 76 118 340 −20 14.4 20% 61.6 6.3

It may be seen that during hydroconversion over Catalyst D, asignificant increase in VI is obtained as compared to thenon-hydroconverted feedstock where both are solvent dewaxed to similarpour points. It may further be seen, based on the amount of dry waxobtained during post-hydroprocessing solvent dewaxing, that asignificant percentage of the wax originally present in the feedstock iseither converted to “oil” or cracked to 350° C.− products by Catalyst Dhydroconversion. The observation that the percentage conversion of waxis significantly greater than the percentage loss of dewaxed oil,coupled with the observed VI increase strongly indicates thatsignificant wax isomerization took place.

Catalyst B Alone

The same waxy feedstock was also hydroconverted/dewaxed using a Pd/Pt onferrierite catalyst (Catalyst B) and in a cascaded reactor sequence ofCatalyst A followed by Catalyst B. Identical reactor pressure andhydrogen flow conditions were used as above. The following 350° C.+product yields and VI's were obtained.

TABLE 2 Reactor Pour Point Yield Temperature (° C.) (%) VI SDW — −22 68112 Catalyst B 310 −20 67 113 320 −26 66 112 330 −32 59 112 340 −38 58111

TABLE 3 Catalyst A followed by Catalyst B Cascaded Reactor ConfigurationPour Temperature Temperature Point Yield 1 2 (° C.) (%) VI SDW — — −2268 112 340 310 −23 57 115 340 310 −21 55 115 340 310 −23 56 114 340 340−35 48 113 340 340 −38 51 113 340 3340 −38 49 113

Here it may be that the stacked bed configuration (cascaded rectorconfiguration) gives dewaxed product with higher VI than that obtainedusing the Catalyst B dewaxing catalyst alone.

The 350 ° C.+ product yields (FIG. 3) and VI's (FIG. 4) as a function ofpour point are compared graphically for the Catalyst B alone and theCatalyst A/Catalyst B stacked bed configuration.

Example 2

This example is directed to a comparison of a 0.5% Pt/silica-aluminacatalyst with a pore volume of 0.54 ml/gm (H₂O), and alumina content of45 wt % based on silica-alumina and an isoelectric point of 5.41(designated Catalyst A) with a 0.5% Pt/Theta-1 based catalyst (CatalystC). The feed is a waxy lubes hydrocracker distillate which was processedat a reactor pressure of 1000 psig hydrogen and a hydrogen flow rate of2500 scf/bbl.

The following graphical presentation of 350° C.+ topped yields and VI's(FIG. 5 and FIG. 6) show a comparison of:

1. A Catalyst A first, Catalyst C second, stacked bed configuration(4.5:1 ratio of Catalyst A:Catalyst C) wherein Catalyst C phase wasadditionally composited with 0.4/% Pt/alumina in a 1:4.5 ratio ofCatalyst C:alumina.

2. A Catalyst C/Catalyst A composited catalyst (4.5:1 ratio of CatalystA:Catalyst C) wherein the bed was additionally diluted with a 0.4%Pt/alumina in a 3.85:3.15 ratio of composite:alumina.

3. An alumina/Catalyst C composited catalyst (3:1 ratio ofalumina:Catalyst C) wherein Catalyst C contained 0.5% Pt and the aluminacontained 0.6% Pt.

In FIG. 5 it may be seen that the highest VI's (as a function of pourpoint are produced by the Catalyst A first stacked bed configuration.Yields for the stacked bed are higher than for a composite catalyst,albeit lower than for a zeolite only single catalyst (FIG. 6).

Example 3

The following example shows a comparison of the 350° C.+ yields and VI'sproduced by a Catalyst A first, Catalyst C second, stacked bedconfiguration as compared to a “reversed stacked bed” with Catalyst Asecond and Catalyst C first.

The data in FIG. 7 (VI vs. pour point)and FIG. 8 (350° C.+ yield vs.pour point) shows that the Catalyst A first configuration gives higherdewaxing activity (obtained in the Catalyst A bed) at equivalent reactortemperatures than does the reversed stacked bed configuration.

The Catalyst A first configuration has an advantage in that keeping alower zeolite bed temperature will extent useful run lengths or allow adesign with a higher zeolite bed space velocity and hence a smaller,less expensive reactor.

Example 4

In this example, a waxy hydrocracker bottoms feedstock designated asLVIS, was hydroconverted over Catalyst A at a reactor pressure of 1000psig of hydrogen at a flow rate of 2500 scf/bbl.

The following data was obtained for hydroconversion using only CatalystA, which does not reduce pour points to the desired levels, follow bysolvent dewaxing (SDW).

TABLE 4 Catalyst A Pour Grams Dry Wax Dewaxed Point Wax in ConvertedCalculated Oil 350° C.+ Reactor after 350° C.+ to Oil or Dewaxed YieldYield Temp. SDW per 100 350° C.− Oil Yield Loss (%) VI (° C.) (° C.)grams feed Products (%) (%) SDW - Waxy Product 99.8 107 Solvent −21 17.8— 82.0 — Dewaxed Hydro-Converted Products 74.5 114 310 −19 9.1 49% 65.416.6 75.6 114 310 −20 10.4 41% 65.2 16.8 83.8 112 300 −15 12.0 32% 71.710.3 83.7 111 300 −24 13.0 27% 70.7 11.3 87.2 111 295 −19 12.9 28% 74.37.7 89.9 110 290 −19 14.4 19% 75.5 6.6 89.2 109 290 −20 16.0 10% 73.28.8 88.8 110 290 −20 17.1  4% 71.8 10.3 91.5 109 290 −21 14.5 18% 77.05.1 90.0 110 290 −18 14.4 19% 75.6 6.4 91.9 110 290 −18 14.6 18% 77.34.7

It may again be seen that during hydroconversion over Catalyst A, asignificant increase in VI is obtained as compared to thenon-hydroconverted feedstock where both are solvent dewaxed to similarpour points. It may further be seen, based on the amount of dry waxobtained during post-hydroprocessing solvent dewaxing, that generally asignificant percentage of the wax originally present in the feedstock iseither converted to “oil” or cracked to 350° C.− products by Catalyst Ahydroconversion. The observation that the percentage conversion of waxis generally greater than the percentage loss of dewaxed oil, coupledwith the observed VI increase strongly indicates that significant waxisomerization took place.

Example 5

In this example, individual balances of hydroconversion reactionproducts generated in Example 4, prior to solvent dewaxing, wereconsolidated to generate two feeds (designated Feed-10 indicated withsolid square and Feed-25 indicated with solid triangles) in sufficientquantity for a second hydroprocessing reaction over dewaxing Catalyst Cand a 0.5% Pt/high silica ferrierite catalyst (designated Catalyst E),as well as the non-hydroprocessed waxy product whose solvent dewaxedproperties are given in Table 5 (designated as Feed-0 indicated by soliddiamonds) (the waxy product was used as a feed without prior solventdewaxing). The properties of the two consolidated feeds and theirdesignations are:

TABLE 5 Feed Properties and Designations Pour % Dry Wax Reactor Pointafter in 350° C. Temp SDW + Composited Feed Designation VI* (° C.) (°C.) Product Feed-10 110 295 −19 15.6 (˜10% Pre-Converted Feed) Feed-25115 310 −19 14.7 (˜25% Pre-Converted Feed) *VI following feed solventdewaxing to −19° C. pour point. Feed was not solvent dewaxed prior touse as a feed for catalytic dewaxing.

The VI as a function of pour point for the conversion of the three feedsover Catalyst C and Catalyst E are shown graphically in FIGS. 9 and 10,respectively. In both FIGS. 9 and 10 solid diamonds represent Feed-0,solid squares represent Feed-10, and solid triangles represent Feed-25.

It may be seen that the combination of pre-isomerization using thespecified class of acidic isomerization catalyst followed by catalyticdewaxing leads to significantly higher VI's than for catalytic dewaxingalone. This remains true for process sequences which include separationof the vapor products from the liquid products before catalytic dewaxingas well as for process sequences which catalytically dewax the entireproduct from the isomerization reaction step.

What is claimed is:
 1. A process for producing a lubricating base oil having good low temperature properties comprises: (a) contacting a hydrocarbon feedstock with an amorphous silica-alumina based isomerization catalyst having a pore volume less than 0.99 ml/gm (H₂O), an alumina content in the range of 35-55 wt % based on silica-alumina and an isoelectric point in the range of 4.5 to 6.5, and a metal hydrogenation component in the presence of hydrogen to at least partially isomerize waxy paraffins in the hydrocarbon feedstock, forming at least a partially isomerized feedstock; and (b) contacting at least a portion of the at least partially isomerized feedstock with a 10 or 12 ring shape selective crystalline molecular sieve catalyst containing a metal hydrogenation component in the presence of hydrogen to at least partially catalytically dewax the feedstock from step (a).
 2. A process for producing a lubricating base oil having good low temperature properties comprises: (a) contacting a hydrocarbon feedstock with an amorphous silica-alumina based isomerization catalyst having a pore volume less than 0.99 ml/gm (H₂O), an alumina content in the range of 35-55 wt % based on silica-alumina wherein the silica-alumina is modified with a rare earth oxide or yttria or boria or magnesia and has an isoelectric point greater than but no more than 2 points greater than that of the base silica-alumina, and a metal hydrogenation component in the presence of hydrogen to at least partially isomerize waxy paraffins in the hydrocarbon feedstock, forming at least a partially isomerized feedstock; and (b) contacting at least a portion of the at least partially isomerized feedstock with a 10 or 12 ring shape selective crystalline molecular sieve catalyst containing a metal hydrogenation component in the presence of hydrogen to at least partially catalytically dewax the feedstock from step (a).
 3. The process of claims 1 or 2 wherein the at least partially isomerized feedstock is stripped of gaseous components prior to step (b).
 4. The process of claims 1 or 2 wherein the crystalline molecular sieve is a metallo silicate or metallo phosphate.
 5. The process of claim 4 wherein the crystalline molecular sieve is a crystalline alumino silicate or crystalline silicoalumino phosphate.
 6. The process of claim 5 wherein the alumino silicate is ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, natural or synthetic ferrierites, mordenite and offretite or ZSM-57.
 7. The process of claim 5 wherein the crystalline molecular sieve is SAPO-11, SAPO-41, SAPO-31, MAPO-11 or MAPO-31.
 8. The process of claim 5 wherein the crystalline molecular sieve is ZSM-5, ZSM-22, ZSM-23, ferrierites or SAPO-11.
 9. The process of claims 1 or 2 further comprising hydrofinishing the at least partially catalytically dewaxed feedstock.
 10. The process of claims 1 or 2 wherein the catalyst of step (b) further comprises an amorphous component.
 11. The process of claims 1 or 2 wherein the amorphous component has an acidity defined by the Kramer/McVicker scale of from 0.5-2.5.
 12. The process of claims 1 or 2 further comprising extracting the at least partially catalytically dewaxed feedstock. 